Contact lenses: GP guide to choice and the complications Patsy Terry BSc, MCOptom, DCLP

Transcription

1 Contact lenses: GP guide to choice and the complications Patsy Terry BSc, MCOptom, DCLP Patsy Terry describes the properties of the various contact lenses available and how to manage the complications that can arise with lens wear. Figure 1. Appropriate hygiene measures are essential with contact lens wear to avoid potentially sight-threatening infections Most individuals who choose to wear contact lenses do so in order to escape from their spectacles for sport or cosmetic reasons. Lenses offer a more natural field of view with reduced peripheral aberration compared to spectacles. For high myopes (over 5.00D short sighted), there may be enhanced visual acuity since the image formed on the retina is larger when the high minus optical correction is in contact with the eye, rather than held slightly away from the eye as it is in spectacles. In secondary care, contact lenses play a role in the management of certain eye conditions. For many patients with irregular corneas, lenses offer the only and certainly the least invasive form of vision rehabilitation available to them. Assessment of patient suitability Key factors in deciding the suitability of contact lenses include: ocular health, in particular lid hygiene, tear quality and corneal health; vision needs and expectations; lifestyle and anticipated wearing times; dexterity; and general health and medications. Lens selection There are broadly soft or rigid lenses. Their relative benefits are summarised in Table 1. The number of contact lens practitioners fitting lenses for extended wear, ie overnight use, has thankfully reduced as the popularity of the single-use disposable lens has increased. Prior to this, extended wear was marketed as the hassle-free lens option. It is now accepted that overnight use compromises corneal physiology and significantly increases the risk of the sight-threatening complication of microbial keratitis. 1-3 Soft lenses Soft lenses are easy to fit to a normal eye, with manufacturers giving the option of one or two curve fittings on a standard diameter for more common prescriptions. The soft lens centres on the cornea and overlaps the limbus by 1mm. It should show detectable movement Prescriber 5 June

2 Relative benefits of rigid over soft lenses superior vision especially for irregular astigmatism lower incidence of microbial keratitis 1 well-fitted lens provides a good tear pump, reducing risk of inflammation Relative benefits of soft over rigid lenses fitting less time consuming easier adaptation and immediate comfort more forgiving in dusty environments less likely to be dislodged therefore better for most sports Table 1. Relative benefits of soft and rigid lenses with blink when viewed with the slit-lamp microscope. Soft lenses are available in a variety of forms. They may be defined by three elements: the optical correction the lens provides the material used frequency of change/disposability. Optical correction Soft lenses are available in spherical prescriptions to correct simple short/long sight, blended bifocal form or soft toric. A toric lens is designed to correct astigmatism. Extra focus power is incorporated into the lens along a certain meridian. The lens is weighted or chamfered so that it consistently maintains itself at a certain orientation on the eye postblink. Material used There are now two fundamentally different soft lens material groups. Conventional soft hydrogel This material has many derivatives. Hydrogels have long been available with a range of water contents from 24 to 70 per cent. It is the water content of the lens material, together with its thickness, that determines the oxygen flow to the cornea. If 70 per cent water content material is manufactured as a thin lens, the lens dehydrates in the eye causing epithelial dryness. For this reason many of the daily disposables are made from a medium water content material. These lenses perform well in open eye wear, but do not allow sufficient transmission of oxygen for safe overnight extended wear. 2 Silicon hydrogel lenses A dramatic change in the field of contact lenses has been the introduction of silicon into soft hydrogel material creating the silicon hydrogel. The silicon component dramatically increases oxygen flow through the lens, thereby theoretically satisfying the oxygen demands of the underlying corneal tissue for extended wear. Corneal hypoxia should no longer be a complication with a silicon hydrogel lens. However, case studies have been published showing that, despite increased oxygen and carbon dioxide flow with these lenses, elements that predispose to microbial infection and inflammatory reactions still occur under the lens. 4 Extended wear is therefore not considered prudent even with this high oxygen transmission lens type. Daily disposable silicon hydrogel lenses have recently been launched into the ever-expanding range of soft lenses available to the contact lens practitioner. Frequency of change/disposability Soft lens technology changed significantly once the disposable lenses could be mass-produced for a standard range of prescriptions, and affordable daily disposable lenses are now widely available. Disposability has obvious benefits as it removes the need for rigorous nightly lens care and the associated complications. Hand hygiene still remains important. More complex daily-wear soft toric lenses and some brands of bifocal soft lenses are available to Forum If you have any issues you would like to air with your colleagues or comments on articles published in Prescriber, the Editor would be pleased to receive them and, if appropriate, publish them on our Forum page. Please send your comments to: The Editor, Prescriber, The Atrium, Southern Gate, Chichester, West Sussex PO19 8SQ, or to prescriber@wiley.com 54 Prescriber 5 June

3 change on a two-weekly or monthly basis. While solutions are still required to be used on lens removal, the frequency of change ensures fewer tear film deposits and a lower incidence of contact lens-induced inflammation. The majority of silicon hydrogel and some medium-water conventional soft hydrogels lenses work well on this change regimen. Rigid contact lenses Typically the rigid lens is about 10mm in diameter and, with good illumination, can be seen floating on the tear film within the confines of the limbus. Lens fit is assessed after instilling a drop of fluorescein, a fluorescent dye, onto the tear film. This dye is excited by blue UV light: where the lens aligns the cornea the image is dark, where it sits clear of the cornea the image is bright green. Lens care All lenses, except single-use daily disposable lenses, need to be cleaned and disinfected overnight. Soft lens solutions tend to be multipurpose. The lenses need to be rubbed and rinsed with the product prior to insertion in a clean case full of fresh solution. Some patients may be advised by their contact lens practitioner to use a separate cleaner to be rinsed off with sterile saline prior to soaking overnight in disinfecting solution. Most rigid lens solutions are designed solely for use with hard lenses. Importantly all lens wearers are warned against the use of tap water with their lenses as there is a proven risk of Acanthamoeba keratitis. Similarly, swimmers are advised to either remove their lenses before entering the water or else to wear tight-fitting goggles. Medications antihistamines Table 2. Systemic medications with the potential to compromise contact lens wear Case hygiene is critical, with a daily clean and frequent replacement recommended. Contact lenses and children Generally it is recommended to wait until a child is 10 years old before fitting contact lenses. At this age they are typically able to demonstrate motivation to take responsibility for their lenses. Rigid lenses often give the best vision but, when sport is a requirement, daily disposables may be a suitable choice. Scleral contact lenses This lens type has application in secondary care for severe dry eye to maintain an artificial tear reservoir in front of the cornea. It is invaluable in providing vision rehabilitation for patients with tilted corneal grafts, or for those with advanced keratoconus. Scleral lenses typically have a diameter of 23-24mm, ie this lens spreads the contact area to the sclera thereby bridging gross corneal irregularities. Systemic drugs and contact lens wear A number of systemic medications have an adverse effect of reducing reduce both aqueous and mucus secretion antioestrogens, eg clomifene generalised reduced lens tolerance 6 antiarrhythmics, eg amiodarone 6 alpha-blockers beta-blockers, eg atenolol antimetabolites tricyclic antidepressants tranquillisers steroids Reported adverse effect reduce tear volume reduced corneal sensation may delay detection of infection suppressed immune response tear secretion. Patients may complain of reduced lens tolerance and slit-lamp examination will show superficial corneal epithelial erosions. The latter make the cornea more predisposed to infection. Table 2 summaries the drugs that may compromise contact lens wear. Patients who are on chronic ocular therapy, eg for glaucoma, should be advised to insert their drops 30 minutes before lens insertion, or else after removal of lenses, thereby avoiding any ocular irritation from the concentration of preservatives within the lens. Figure 2. In the absence of corneal involvement, bacterial conjunctivitis can be treated with antimicrobial drops such as chloramphenicol SPL Prescriber 5 June

4 Figure 3. Microbial keratitis; arrow shows large corneal infiltrate Management of complications Conjunctivitis Patients should be counselled to remove their lenses as soon as there is any sign of conjunctivitis (see Figure 2). It is important to exclude any involvement of the cornea by slit-lamp examination. In the absence of corneal involvement, antimicrobial drops, eg chloramphenicol, may be prescribed with an instruction to return if there is no resolution or worsening of the condition. Old lenses, lens cases and solutions should be discarded. Hygiene should be reviewed prior to return to any lens wear. Microbial keratitis The differential diagnosis between microbial keratitis (see Figure 3)and a benign complication of lens wear is critical. Microbial keratitis is the acute and potentially blinding condition where bacteria invade the cornea. The patient often needs hospitalisation. There is risk of perforation and endophthalmitis (inflammation of internal structures) if treatment is inappropriate or delayed. There is often residual corneal scarring, and this has significant impact on vision if the scar tissue is near the visual axis. Table 3 outlines the differential diagnosis of microbial keratitis and sterile keratitis/contact lens-induced peripheral ulcer. The latter will resolve on cessation of lens wear. Parameter Microbial keratitis Sterile infiltrate/clpu symptoms ++ + lid swelling ++ +/- conjunctival redness generalised typically localised infiltrate shape round infiltrate size >1mm <1mm fluorescein staining ++ - surrounding cornea severe hazy clear/slight haze effects of lens discontinuation no change/worse resolving modified from Aasuri et al CLPU = contact lens-induced peripheral ulcer Table 3. Differential diagnosis of microbial keratitis and sterile corneal inflammation The immune-compromised or diabetic patient can be particularly prone to keratitis and needs to be counselled to remove lenses at the first signs of redness. Patients should also avoid wearing lenses if they have an upper respiratory tract infection or herpetic lesions on the face. Differentiation cannot be made without a slit lamp. If there is any doubt, referral is indicated as a matter of urgency for expert attention. Ophthalmologists ideally take corneal scrapes prior to commencement of any treatment. If corneal involvement is suspected many optometrists will refer directly to the eye casualty and inform the GP, thereby expediting the start of appropriate treatment. Clarity on preferred local pathways for referral is imperative. Lost lenses Occasionally a soft lens may fold and hide itself under the top lid. With the patient resting their head back and fixating a target on the floor, retract the lid, without everting, and inspect the superior area of the globe. The edge should just be visible. A drop of fluorescein will stain the lens yellow and make detection even easier. Slide the lens down and pinch out. A rigid lens may bind to the bulbar conjunctiva. To break the suction, manipulate the edge of the lid under the edge of the lens. A blunt fine instrument may help take care near the cornea. Summary Contact lenses offer a superior form of vision correction for many individuals. Lenses are medical devices and a risk of eye infection with sight-threatening consequence exists. However, with appropriate hygiene measures, careful selection of patients and 56 Prescriber 5 June

5 regular aftercare with their contact lens practitioner, there should be no reason for complications arising from lens wear to present to the GP practice. A slit-lamp microscope is critical in the differential diagnosis of any contact lens-induced complication. A good relationship with local primary care optometrists, who have a special interest in contact lenses and ocular therapeutics, will be valuable to assist in timely and appropriate onward referral. References 1. Stapleton F, et al. Contact Lens Association of Ophthalmologists Journal 1993;19: Holden BA, et al. Ophthalmology and Vision Science 1984;25: Efron N. Contact lens complications, 2nd ed. Butterworth Heinemann, Lim L, et al. British Journal of Ophthalmology 2002;86(3): Aasuri MK, et al. Eye Contact Lens 2003;9(suppl 1):S Electronic medicines information for optometrists (E med info). Compiled by Professor Lawrenson and David Thomson, Ms Terry is head optometrist, Oxford Eye Hospital Prescriber 5 June